Conventionally, electrolytic capacitors comprise a case with an open top end and a closed bottom end, a cartridge impregnated with an electrolyte therein, and a molded dielectric header used in combination with an elastomeric or rubber gasket for sealing the open end of the case and encapsulating the impregnated cartridge there within. The impregnated cartridge, also to be referred to as the capacitor section hereinafter, is conventionally made up of a series of layers which include a first aluminum foil coated with a layer of aluminum oxide, a paper separator, a second layer of aluminum and a farther layer of paper. The assembled layers are spirally wound to form an elongated cylinder which is impregnated with an electrolyte solution. This capacitor section is contained within the case, which is normally of aluminum material. The upper end of the capacitor section includes first and second tabs connected respectively to the first and second layers of foil to provide anode and cathode connections. The tabs, in turn, are connected within the case to terminals extending through a molded capacitor header that serves to cover the open end of the capacitor case.
A rubber gasket is inserted between the circumferential edges of the molded capacitor header and the capacitor case and afterwards, the top end of the open capacitor case is crimped or rolled over towards the inside of the case to cause the molded capacitor header to be forced tight against a ledge inside the capacitor case, thereby providing a sealed closure of the open end of the capacitor case.
In one type of capacitor which has been available in the field for years, the capacitor case is made of aluminum material, the header is made of phenolic or similar thermosetting material, and the electrolyte is of a glycol type. While such capacitors have performed well over the years, the market requires small and large capacitors to perform in environments where the temperature exceeds 85.degree. C. This requirement creates the need and demand for capacitors of small and large size which are capable of operating at high temperatures and maintaining a reliable seal.
The conventional capacitor described above is limited in its use to environments in which the temperature is less than 85.degree. C. The glycol type electrolyte used in such capacitors requires significant amounts of water, and with exposure of such capacitors to higher temperatures, the water tends to hydrate the foils with consequent injury to the capacitor.
In an attempt to provide a capacitor of smaller size with operating capabilities which are at least the equivalent of the glycol capacitor, the field has turned to the use of new types of electrolytes which will operate reliably in environments of higher temperature. However, while such electrolytes are known to have inherent characteristics and advantages, it has been found that the header and the rubber seals of the conventional capacitors have a short life. After a period of use at high temperatures, the materials of the header and the gasket swell and become soggy, hence, causing leakage and sealing problems.
Manufactures have provided headers for small and large diameter capacitors which withstand electrolytes that operate reliably in environments of higher temperatures, but capacitors employing these headers and electrolytes in temperatures greater than 85.degree. C., still have problems with the deterioration of the rubber gasket and the weakening of the seal it provides between the header and the case.